Stereoselective pharmacokinetics of stable isotope (+/-)-[13C]-pantoprazole: Implications for a rapid screening phenotype test of CYP2C19 activity

A comparative study of chiral separation of proton pump inhibitors by supercritical fluid chromatography and high-performance liquid chromatography

A comparative study of chiral separation of pantoprazole and rabeprazole is carried out using supercritical fluid chromatography and high-performance liquid chromatography. The columns used were Chiralpak IA and Chiralpak IE. The best mobile phase in supercritical fluid chromatography was carbon dioxide-0.2% triethylamine in methanol (60:40) and 0.1% triethylamine in n-hexane-ethanol (50:50) in high-performance liquid chromatography. For supercritical fluid chromatography, values of the retention factor of pantoprazole enantiomers were 3.97 and 4.88. These values for rabeprazole enantiomers were 6.10 and 7.52. The values of separation and resolution factor for pantoprazole and rabeprazole were 1.23 and 1.23 and 2.20 and 3.36, respectively. Similarly, for high-performance liquid chromatography, the values of retention factor for enantiomers of pantoprazole were 4.02 and 7.32. These values for rabeprazole enantiomers were 5.32 and 7.88, respectively. The values of separation and resolution factor for pantoprazole and rabeprazole were 1.82 and 1.48 and 9.22 and 6.58, respectively. A comparison was carried out, which confirmed supercritical fluid chromatography as the best method due to its fastness, eco-friendly, and inexpensiveness. The reported methods are effective, efficient, and reproducible and may be used to separate and identify pantoprazole and rabeprazole in any unknown samples.

Point-of-care companion diagnostic tests for personalizing psychiatric medications: fulfilling an unmet clinical need

Over the last decade stable isotope-labeled substrates have been used as probes for rapid, point-of-care, non-invasive and user-friendly phenotype breath tests to evaluate activity of drug metabolizing enzymes. These diagnostic breath tests can potentially be used as companion diagnostics by physicians to personalize medications, especially psychiatric drugs with narrow therapeutic windows, to monitor the progress of disease severity, medication efficacy and to study in vivo the pharmacokinetics of xenobiotics. Several genotype tests have been approved by the FDA over the last 15 years for both cytochrome P450 2D6 and 2C19 enzymes, however they have not been cleared for use in personalizing medications since they fall woefully short in identifying all non-responders to drugs, especially for the CYP450 enzymes. CYP2D6 and CYP2C19 are among the most extensively studied drug metabolizing enzymes, involved in the metabolism of approximately 30% of FDA-approved drugs in clinical use, associated with large individual differences in medication efficacy or tolerability essentially due to phenoconversion. The development and commercialization via FDA approval of the non-invasive, rapid (<60 min), in vivo, phenotype diagnostic breath tests to evaluate polymorphic CYP2D6 and CYP2C19 enzyme activity by measuring exhaled ¹³CO₂ as a biomarker in breath will effectively resolve the currently unmet clinical need for individualized psychiatric drug therapy. Clinicians could personalize treatment options for patients based on the CYP2D6 and CYP2C19 phenotype by selecting the optimal medication at the right initial and subsequent maintenance dose for the desired clinical outcome (i.e. greatest efficacy and minimal side effects).

Metabolic profiling of myrislignan by UPLC-ESI-QTOFMS-based metabolomics

The metabolic map of myrislignan was determined by UPLC-ESI-QTOFMS-based metabolomics in vivo and in vitro.

Application of a high-throughput, parallel HPLC system for quantitative chiral analysis of pantoprazole

Background: Chromatographic separation of enantiomers is considered a task in analytical chemistry particularly for high sample throughput. This paper describes a high-throughput parallel HPLC–MS/MS method for the determination of pantoprazole enantiomers. Results: Baseline separation of pantoprazole enantiomers was achieved on a Chiralcel OZ-RH column in a run time of 4.5 min. Assays for enantiomers were linear with satisfactory intra- and inter-day precision and accuracy. The assay was suitable for high-throughput analysis as shown by its successful application to a chiral PK study in beagle dog. Conclusion: A high-throughput parallel HPLC–MS/MS assay for pantoprazole has been developed and validated. This method provides nearly twofold increased sample throughput, and was shown to be suitable for application in PK studies.

CYP2C19 Phenoconversion by Routinely Prescribed Proton Pump Inhibitors Omeprazole and Esomeprazole: Clinical Implications for Personalized Medicine

The phenotype pantoprazole-(13)C breath test (Ptz-BT) was used to evaluate the extent of phenoconversion of CYP2C19 enzyme activity caused by commonly prescribed proton pump inhibitors (PPI) omeprazole and esomprazole. The Ptz-BT was administered to 26 healthy volunteers and 8 stable cardiovascular patients twice at baseline and after 28 days of PPI therapy to evaluate reproducibility of the Ptz-BT and changes in CYP2C19 enzyme activity (phenoconversion) after PPI therapy. The average intrapatient interday variability in CYP2C19 phenotype (n = 31) determined by Ptz-BT was considerably low (coefficient of variation, 17%). Phenotype conversion resulted in 25 of 26 (96%) nonpoor metabolizer (non-PM) volunteers/patients as measured by the Ptz-BT at baseline and after PPI therapy. The incidence of PM status by phenotype following administration of omeprazole/esomeprazole (known inhibitors of CYP2C19) was 10-fold higher than those who are genetically PMs in the general population, which could have critical clinical implications for personalizing medications primarily metabolized by CYP2C19, such as clopidogrel, PPI, cyclophosphamide, thalidomide, citalopram, clonazepam, diazepam, phenytoin, etc. The Ptz-BT can rapidly (30 minutes) evaluate CYP2C19 phenotype and, more importantly, can identify patients with phenoconversion in CYP2C19 enzyme activity caused by nongenetic factors such as concomitant drugs.

In vitro metabolism of the lignan (-)-grandisin, an anticancer drug candidate, by human liver microsomes

(-)-grandisin is a tetrahydrofuran lignan that displays important biological properties, such as trypanocidal, anti-inflammatory, cytotoxic, and antitumor activities, suggesting its utility as a potential drug candidate. One important step in drug development is metabolic characterization and metabolite identification. To perform a biotransformation study of (-)-grandisin and to determine its kinetic properties in humans, a high performance liquid chromatography (HPLC) method was developed and validated. After HPLC method validation, the kinetic properties of (-)-grandisin were determined. (-)-grandisin metabolism obeyed Michaelis-Menten kinetics. The maximal reaction rate (Vmax ) was 3.96 ± 0.18 µmol/mg protein/h, and the Michaelis-Menten constant (Km ) was 8.23 ± 0.99 μM. In addition, the structures of the metabolites derived from (-)-grandisin were characterized via gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) analysis. Four metabolites, 4-O-demethylgrandisin, 3-O-demethylgrandisin, 4,4'-di-O-demethylgrandisin, and a metabolite that may correspond to either 3,4-di-O-demethylgrandisin or 3,5-di-O-demethylgrandisin, were detected. CYP2C9 isoform was the main responsible for the formation of the metabolites. These metabolites have not been previously described, demonstrating the necessity of assessing (-)-grandisin metabolism using human-derived materials.

Is (+)-[13C]-pantoprazole better than (±)-[13C]-pantoprazole for the breath test to evaluate CYP2C19 enzyme activity?

Recently, we have shown that the (+)-[(13)C]-pantoprazole is more dependent on CYP2C19 metabolic status than (-)-[(13)C]-pantoprazole. In this study, we tested the hypothesis that (+)-[(13)C]-pantoprazole is a more sensitive and selective probe for evaluating CYP2C19 enzyme activity than the racemic mixture. (+)-[(13)C]-pantoprazole (95 mg) was administered orally in a sodium bicarbonate solution to healthy volunteers. Breath and plasma samples were collected before and up to 720 min after dosing. The (13)CO2 in exhaled breath samples was measured by infrared spectrometry. Ratios of (13)CO2/(12)CO2 after (+)-[(13)C]-pantoprazole relative to (13)CO2/(12)CO2 at baseline were expressed as delta over baseline (DOB). (+)-[(13)C]-pantoprazole concentrations were measured by HPLC. Genomic DNA extracted from whole blood was genotyped for CYP2C19*2, *3 and *17 using Taqman assays. Statistically significant differences in the area under the plasma concentration time curve (AUCplasma(0-∞) (p < 0.001) and oral clearance (<0.01) of (+)-[(13)C]-pantoprazole as well as in the breath test indices (delta over baseline, DOB30; and area under the DOB versus time curve, AUCDOB(0-120)) (p < 0.01) were observed among poor, intermediate and extensive metabolizer of CYP2C19. DOB30 and AUCDOB(0-120) adequately distinguished poor metabolizer from intermediate and extensive metabolizer of CYP2C19. Breath test indices significantly correlated with plasma elimination parameters of (+)-[(13)C]-pantoprazole (Pearson correlations: -0.68 to -0.73). Although relatively higher breath test indices were observed after administration of (+)-[(13)C]-pantoprazole (this study) than after (±)-[(13)C]-pantoprazole (previous study), the performance of the racemic and the enantiomer as marker of CYP2C19 activity remained similar. Our data confirm that the metabolism of (+)-[(13)C]-pantoprazole is highly dependent on CYP2C19 metabolic status, but the breath test derived from it is not superior to the racemic [(13)C]-pantoprazole in evaluating CYP2C19 activity in vivo. Thus, racemic [(13)C]-pantoprazole which is relatively easy to synthesize and more stable than (+)-[(13)C]-pantoprazole is adequate as a probe of this enzyme.

Individualized therapy for gastroesophageal reflux disease: potential impact of pharmacogenetic testing based on CYP2C19

The main therapeutic agent for gastroesophageal reflux disease (GERD) is a proton pump inhibitor (PPI). Plasma levels and the acid inhibitory effect of PPIs depend on the activity of cytochrome P450 (CYP) 2C19, which is polymorphic. Genotypes of CYP2C19 are classified into three groups: rapid metabolizers (RMs: *1/*1), intermediate metabolizers (IMs: *1/*X), and poor metabolizers (PMs: *X/*X), where *1 and X represent the wild type and the mutant allele, respectively. RMs include ultra-rapid metabolizers, who possess the CYP2C19*17 allele. The pharmacokinetics and pharmacodynamics of PPIs differ among different CYP2C19 genotype groups. Plasma PPI levels and intragastric pH values during PPI treatment are lowest in the RM group, intermediate in the IM group, and highest in the PM group. These CYP2C19-genotype-dependent differences in the pharmacokinetics and pharmacodynamics of PPIs influence the healing and recurrence of GERD during PPI treatment, suggesting the need for CYP2C19 genotype-based tailored therapy for GERD. CYP2C19 pharmacogenetics should be taken into consideration for the personalization of PPI-based therapy. However, the clinical usefulness of CYP2C19 genotype testing in GERD therapy should be verified in clinical studies.

Individualized therapy for gastroesophageal reflux disease: potential impact of pharmacogenetic testing based on CYP2C19

The main therapeutic agent for gastroesophageal reflux disease (GERD) is a proton pump inhibitor (PPI). Plasma levels and the acid inhibitory effect of PPIs depend on the activity of cytochrome P450 (CYP) 2C19, which is polymorphic. Genotypes of CYP2C19 are classified into three groups: rapid metabolizers (RMs: *1/*1), intermediate metabolizers (IMs: *1/*X), and poor metabolizers (PMs: *X/*X), where *1 and X represent the wild type and the mutant allele, respectively. RMs include ultra-rapid metabolizers, who possess the CYP2C19*17 allele. The pharmacokinetics and pharmacodynamics of PPIs differ among different CYP2C19 genotype groups. Plasma PPI levels and intragastric pH values during PPI treatment are lowest in the RM group, intermediate in the IM group, and highest in the PM group. These CYP2C19-genotype-dependent differences in the pharmacokinetics and pharmacodynamics of PPIs influence the healing and recurrence of GERD during PPI treatment, suggesting the need for CYP2C19 genotype-based tailored therapy for GERD. CYP2C19 pharmacogenetics should be taken into consideration for the personalization of PPI-based therapy. However, the clinical usefulness of CYP2C19 genotype testing in GERD therapy should be verified in clinical studies.

Impact of genetic polymorphisms in CYP2C9 and CYP2C19 on the pharmacokinetics of clinically used drugs

Human cytochrome P450 (CYP) is a superfamily of hemoproteins which oxidize a number of endogenous compounds and xenobiotics. The human CYP2C subfamily consists of four members: CYP2C8, CYP2C9, CYP2C18 and CYP2C19. CYP2C9 and CYP2C19 are important drug-metabolizing enzymes and together metabolize approximately 20% of therapeutically used drugs. Forty-two allelic variants for CYP2C9 and 34 for CYP2C19 have been reported. The frequencies of these variants show marked inter-ethnic variation. The functional consequences of genetic polymorphisms have been examined, and many studies have shown the clinical importance of these polymorphisms. Current evidence suggests that taking the genetically determined metabolic capacity of CYP2C9 and CYP2C19 into account has the potential to improve individual risk/benefit relationships. However, more prospective studies with clinical endpoints are needed before the paradigm of "personalized medicine" based on the variants can be established. This review summarizes the currently available important information on this topic.